One important aim in the development of power transistors is to produce transistors with a high voltage blocking capability but, nevertheless, a low on-resistance (RON) and which have low switching losses.
Power transistors usually include a drift region arranged between a body region and a drain region and doped lower than the drain region. The on-resistance of a conventional power transistor is dependent on the length of the drift region in current flow direction and on the doping concentration of the drift region, wherein the on-resistance decreases when the length of the drift region is reduced or when the doping concentration in the drift region is increased. However, reducing the length of the region or increasing the doping concentration reduces the voltage blocking capability.
One possible way to reduce the on-resistance of a power transistor for a given voltage blocking capability is to provide compensation regions in the drift region, wherein the compensation regions are doped complementary to the drift region. Another possible way is to provide field plates in the drift region which are dielectrically insulated from the drift region and which are, for example, connected to a gate or source terminal of the transistor. In these types of power transistors, the compensation zones or the field plates partly “compensate” doping charges in the drift region when the component is in its off-state. This allows a higher doping of the drift region, which reduces the on-resistance, without reducing the voltage blocking capability.
These known transistors, however, have a high output capacitance. There is, therefore a need to provide a power transistor with a high voltage blocking capability, a low on-resistance and a low output capacitance.